Method for fabricating an aperture

ABSTRACT

A method for fabricating an aperture is disclosed. The method includes the steps of: forming a hard mask containing carbon on a surface of a semiconductor substrate; and using a non-oxygen element containing gas to perform a first etching process for forming a first aperture in the hard mask. Before forming the hard mask, a gate which includes a contact etch stop layer and a dielectric layer is formed on the semiconductor substrate.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a Continuation Application of U.S. patent application Ser. No. 13/156,319, which was filed on Jun. 8, 2011, the entire contents of which are incorporated herein by this reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a method for fabricating an aperture, and more particularly, to a method for fabricating an aperture in a hard mask while preventing the occurrence of a bowing profile on a sidewall of the hard mask.

2. Description of the Prior Art

The trend towards micro-miniaturization, or the ability to fabricate semiconductor devices with features smaller than 0.1 micrometers, has presented difficulties when attempting to form narrow diameter, deep (high aspect ratio) contact holes in a dielectric layer, to expose underlying conductive regions.

The conventional approach of fabricating contact holes typically involves providing a semiconductor substrate with a plurality of semiconductor devices thereon, in which the semiconductor devices includes MOS transistors or resistors. At least a dielectric layer and a hard mask are then formed on the semiconductor substrate to cover the semiconductor devices, and a patterned resist is used to perform a series of pattern transfer processes to form a contact hole in the hard mask and the dielectric layer.

The conventional method typically uses an oxygen containing gas for performing the aforementioned pattern transfer process, which causes severe indentation with respect to the central region of the sidewall and ultimately produces a bowing profile. Unfortunately, metal deposited in the contact hole thereafter is likely to seal the entrance of the hole before filling the expanding bowing portion of the contact hole. As a result, a seam is formed relative to the central region of the deposited metal, which degrades the electrical connection of the device and affects the overall performance.

SUMMARY OF THE INVENTION

It is an objective of the present invention to provide a method for resolving the issue of bowing profile in the contact hole fabricated by conventional technique.

According to a preferred embodiment of the present invention, a method for fabricating an aperture is disclosed. The method includes the steps of: forming a hard mask containing carbon on a surface of a semiconductor substrate; and using a non-oxygen element containing gas to perform a first etching process for forming a first aperture in the hard mask.

Another aspect of the present invention provides a method for fabricating an aperture. The method includes the steps of: forming a hard mask and a dielectric anti-reflective coating (DARC) on a semiconductor substrate; forming a first bottom anti-reflective coating (BARC) on the DARC; forming a first aperture in the first BARC and portion of the DARC; forming a second BARC on the DARC and filling the first aperture; forming a second aperture in the second BARC and portion of the DARC; and using a non-oxygen element containing gas to perform an etching process to transfer the first aperture and the second aperture to the hard mask for forming a plurality of third apertures.

Another aspect of the present invention provides a method for fabricating an aperture, which includes the steps of: forming a hard mask and a dielectric anti-reflective coating (DARC) on a semiconductor substrate; forming a first bottom anti-reflective coating (BARC) on the DARC; etching the first BARC, the DARC, and the hard mask for forming a first aperture in the hard mask; forming a second BARC on the DARC to fill the first aperture; and etching the second BARC, the DARC, and the hard mask to forma second aperture in the hard mask, wherein the step of etching the hard mask comprises using a non-oxygen element containing gas.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-3 illustrate a method for fabricating an aperture according to a preferred embodiment of the present invention.

FIGS. 4-5 illustrate a method for fabricating an aperture according to another embodiment of the present invention.

FIGS. 6-11 illustrate a method for fabricating an aperture according to another embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIGS. 1-3, which illustrate a method for fabricating an aperture according to a preferred embodiment of the present invention. As shown in FIG. 2, a semiconductor substrate 60, such as a substrate composed of monocrystalline silicon, gallium arsenide (GaAs) or other known semiconductor material is provided. A standard metal-oxide semiconductor (MOS) transistor fabrication is performed to form at least one MOS transistor (not shown) or other semiconductor devices on the semiconductor substrate 60. The MOS transistor could be a PMOS transistor, an NMOS transistor, or a CMOS transistor, and the MOS transistor could also include typical transistor structures including a gate structure, a spacer, a lightly doped drain, a source/drain regions and/or salicides. The gate structure could be a polysilicon gate or a metal gate fabricated from a high-k first or high-k last processes. As these processes are well known to those skilled in the art, the details thereof are omitted for the sake of brevity.

A contact etch stop layer (CESL) 34 composed of nitrides is then deposited on the MOS transistors, in which the depth of the contact etch stop layer 34 is about 850 Angstroms. The contact etch stop layer 34 could be formed selectively, and the contact etch stop layer 34 could be formed to provide stress to the device underneath. For instance, the contact etch stop layer 34 could be a SiC layer providing tensile stress for NMOS transistors, or a SiN layer providing compressive stress for PMOS transistors. If a STI or non-transistor device is disposed underneath, the contact etch stop layer could be a composite contact etch stop layer consisting of tensile CESL and compressive CESL, and a buffer layer is further inserted between the tensile CESL and the compressive CESL.

An interlayer dielectric layer (ILD) 36 is formed on the surface of the contact etch stop layer 34. In this embodiment, the interlayer dielectric layer 36 is preferably composed of three layers, including a dielectric layer deposited by sub-atmospheric pressure chemical vapor deposition (SACVD), a phosphosilicate glass (PSG) layer, and a tetraethylorthosilicate (TEOS) layer. The depth of the entire interlayer dielectric layer 36 is a few thousand Angstroms (preferably approximately 3150 Angstroms); the depth of the dielectric layer is around several thousands of Angstroms (preferably 250 Angstroms); the depth of the PSG layer is between 1000 Angstroms to 3000 Angstroms (preferably 1900 Angstroms); and the depth of the TEOS layer is between 100 Angstroms to 2000 Angstroms (preferably 1000 Angstroms). In addition to being a composite material layer, the interlayer dielectric layer 36 could also be a single material layer, and in addition to the aforementioned materials, the interlayer dielectric layer 36 could also include undoped silicate glass (USG), borophosposilicate glass (BPSG), low-k dielectric material such as porous dielectric material, SiC, SiON, or any combination thereof.

A hard mask 44 is then formed on the surface of the interlayer dielectric layer 36. According to a preferred embodiment of the present invention, the hard mask 44 is composed of a carbon containing material such as amorphous carbon, and is preferably selected from an advanced pattern film (APF) fabricated by Applied Materials Inc., in which the depth of the hard mask 44 is between 1000 Angstroms to 5000 Angstroms, and preferably 2000 Angstroms. A dielectric anti-reflective coating (DARC) 46 and a bottom anti-reflective coating (BARC) 48 are then deposited on the surface of the hard mask 44. In this embodiment, the DARC 46 is preferably composed of a silicon oxynitride (SiON) layer and an oxide layer, in which the depth of the DARC 46 is approximately 250 Angstroms, and the depth of the BARC 48 is approximately 1020 Angstroms. The DARC 46 and the BARC 48 are formed selectively, and in addition to inorganic materials, these two layers 46 and 48 could also be composed of organic materials by a spin-coating process.

A plurality of pattern transfer processes is then performed on the above stacked film to form an aperture penetrating the BARC 48, the DARC 46, the hard mask 44, the interlayer dielectric layer 36, and the contact etch stop layer 34 to expose the MOS transistor underneath, such as the source/drain region of the MOS transistor. For example, a patterned resist 54 adapted for a wavelength of approximately 193 nm is formed on the aforementioned stacked film to expose a portion of the upper surface of the BARC 48, in which the depth of the patterned resist 54 is approximately 1800 Angstroms. A descum process is performed thereafter by using a gas containing CO and O₂ to remove excessive particles produced from the exposure and development process.

Next, as shown in FIG. 2, the patterned resist 54 is used as a mask to perform a pattern transfer process on the BARC 48. Preferably, an etching gas containing CF₄ and CH₂F₂ is utilized to remove a portion of the BARC 48 and the DARC 46 for transferring the aperture pattern of the patterned resist 54 to the BARC 48 and the DARC 46 and exposing the hard mask 44 underneath.

As shown in FIG. 3, another pattern transfer is performed by using the patterned resist 54 as a mask and non-oxygen element containing gas as an etching gas to partially remove the hard mask 44. This transfers the aperture in the BARC 48 and the DARC 46 to the hard mask 44 for forming a patterned hard mask. In this embodiment, the non-oxygen element containing etching gas utilized is selected from a group consisting of H₂, N₂, He, NH₃, CH₄, and C₂H₄. It should also be noted that, as the non-oxygen element containing gas is used to pattern the hard mask 44, the patterned resist 54 and the BARC 48 above the hard mask 44 are also removed simultaneously to form an aperture 56 in the hard mask 44.

Next, the patterned hard mask 44 is used as a mask to perform an etching process on the ILD 36 and the CESL 34, such as using a gas containing C₄F₆, O, and Ar to partially remove the ILD 36, thereby transferring the aperture 56 to the ILD 36 and the CESL 34. This completes the fabrication of an aperture according to a preferred embodiment of the present invention.

As current fabrication processes typically cannot obtain a desirable aperture pattern from one single pattern transfer process due to smaller pitch, a two exposure and two development (2P2E) approach is often employed to form desirable aperture patterns. Please refer to FIGS. 4-5, which illustrate perspective views of applying the aforementioned method for forming apertures to a current 2P2E process according to another embodiment of the present invention.

As shown in FIG. 4, after the aperture 56 is formed in the hard mask 44 of FIG. 3, another BARC 62 and a patterned resist 64 may be formed on the DARC 46, in which the BARC 62 preferably fills the aperture 56 entirely.

As shown in FIG. 5, an etching process is performed by first using the patterned resist 64 as a mask to partially remove the BARC 62 and the DARC 46 for exposing the hard mask 44 underneath. Next, another etching process is carried out by using a non-oxygen element containing gas to etch the hard mask 44. This transfers the aperture of the BARC 62 and the DARC 46 to the hard mask 44 for forming a patterned hard mask. After stripping the patterned resist 62, the BARC 62 and the DARC 46, an etching process is carried out by using the patterned hard mask 44 directly as a mask to partially remove the ILD 36 and the CESL 34.

Please refer to FIGS. 6-11, which illustrate perspective views of applying the aforementioned method of forming apertures to a 2P2E process according to another embodiment of the present invention. As shown in FIG. 6, a semiconductor substrate 80 is provided, in which at least one semiconductor device (not shown) is formed on the semiconductor substrate 80. The semiconductor device could be a MOS transistor, such as a PMOS transistor, an NMOS transistor, or a CMOS transistor, or devices of other types.

A CESL 82, an ILD 84, a hard mask 86, a DARC 88, a first BARC 90, and a patterned resist 92 are sequentially formed on the semiconductor device. The materials of the CESL 82, the ILD 84, the hard mask 86, the DARC 88, and the first BARC 90 could be analogous to the ones disclosed in the aforementioned embodiments; the details are therefore omitted for the sake of brevity.

Next, a pattern transfer process is performed by using the patterned resist 92 as a mask and using an etching gas containing CF₄ and CH₂F₂ to partially remove the first BARC 90 and a portion of the DARC 88. In this embodiment, this etching process preferably removes only half the thickness of the DARC 88 while not exposing any of the hard mask 86 underneath. After stripping the patterned resist 92 and the remaining first BARC 90, as shown in FIG. 7, a first aperture 94 is formed in the DARC 88.

As shown in FIG. 8, a second BARC 96 and a patterned resist 98 are sequentially formed on the DARC 88, in which the second BARC 96 preferably fills the first aperture 94 in the DARC 88. Next, as shown in FIG. 9, another pattern transfer process is performed by using the patterned resist 98 as a mask to partially remove the second BARC 90 and half the thickness of the DARC 88 while not exposing any of the hard mask 86 underneath. After stripping the patterned resist 98 and the remaining second BARC 96, a second aperture 100 is formed in the DARC 88.

As shown in FIG. 10, an etching process is first carried out to remove the remaining DARC 88 under the first aperture 94 and the second aperture 100 to expose the hard mask 86, and another etching process is performed by using the remaining DARC 88 as a mask to form a plurality of third apertures 102 in the hard mask 66. Similar to the aforementioned embodiment for etching the hard mask 86, this embodiment also uses a non-oxygen element containing gas to partially remove the hard mask 86 for forming the third apertures 102, in which the non-oxygen element gas utilized is selected from a group consisting of H₂, N₂, He, NH₃, CH₄, and C₂H₄.

Next, as shown in FIG. 11, an etching process is conducted by using the remaining DARC 88 as a mask, or first removing the remaining DARC 88 and using the patterned hard mask 86 as a mask to transfer the third apertures 102 in the hard mask 86 to the ILD 86 and the CESL 82. This completes the fabrication of apertures according to the embodiment of the present invention. It should be noted that the apertures formed through the aforementioned embodiments are not limited to circular apertures, but could also be formed along the horizontal axis of the gate to form rectangular slot openings; and, after metals are filled into these rectangular slot openings, rectangular contact plugs are formed.

Overall, the present invention uses a non-oxygen element containing gas to etch a hard mask of a stacked film for forming desirable aperture patterns. According to a preferred embodiment of the present invention, the hard mask is preferably selected from an advanced pattern film (APF) fabricated by Applied Materials Inc., and the non-oxygen element gas is selected from a group consisting of H₂, N₂, He, NH₃, CH₄, and C₂H₄. As conventional methods of using CO/O₂/CO₂ based etching gas typically cause issues such as side etching in the hard mask and aperture shrinkage, the present invention specifically uses a non-oxygen element containing gas for conducting the etching process to maintain an adequate hard mask profile and critical dimension uniformity. Moreover, as critical dimensions decrease, the approach of the present invention also maintains a consistent vertical profile of the aperture and prevents problems such as hole distortion.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

What is claimed is:
 1. A method for fabricating an aperture, comprising: forming a hard mask containing amorphous carbon on a surface of a semiconductor substrate; and using a non-oxygen element containing gas to perform a first etching process for forming a first aperture in the hard mask, wherein the non-oxygen element containing gas consists of H₂ and N₂.
 2. The method of claim 1, wherein after forming the hard mask comprises: forming a dielectric anti-reflective coating, a bottom anti-reflective coating, and a patterned resist on the hard mask; using the patterned resist to perform a second etching process for forming a second aperture in the bottom anti-reflective coating and the dielectric anti-reflective coating; and using the patterned resist to perform the first etching process for forming the first aperture in the hard mask.
 3. The method of claim 1, further comprising forming agate structure on the semiconductor substrate before forming the hard mask, wherein the gate structure comprises a contact etch stop layer and a dielectric layer thereon.
 4. The method of claim 3, wherein the gate structure comprises a polysilicon gate or a metal gate.
 5. The method of claim 3, further comprising using the first aperture to define a rectangular slot opening along the horizontal axis of the gate structure. 